Metal diaphragm unit



Nov. 9, 1954 G. B, BAlLEY METAL DIAPHRAGM UNIT Original Filed June 24,1948 llvvmvrok; 6502a: 6.15A/LEY.

ATTOIA/EYS/ United States Patent METAL DIAPHRAGM UNIT George B. Bailey,San Mateo, Calif., assignor to The Hays Corporation, Michigan City,Ind., a corporation of Indiana Original application June 24, 1948,Serial No. 34,960. Divided and this application August 15, 1950, Sena]No. 179,566

1 Claim. (Cl. 137-795) This invention relates to improvements in metaldiaphragm units particularly suited for use in fluid pressure au es. g The primary object of the invention is to provide a novel diaphragm unitfor a fluid pressure gauge which employs an unbonded strain gauge as themeasuring element thereof. g

A further object is to provide a novel diaphragm unit for a device ofthis character wherein a fluid, preferably a dielectric fluid such asoil, serves as the pressure transmitting means to prevent contact of themeasuring element with any conductor and to prevent access of condensateto the measuring element.

A further object is to provide a device of this character which is soconstructed as to avoid any error due to extraneous conditions, ture ordifferences in the rate of effect of changes in temperature in differentparts of the unit.

A further object is to provide a device of this character having ameasuring diaphragm of novel construction and novel mounting.

A further object is to provide a device of this character which may beutilized either to measure static pressure or to measure the differenceof two pressures.

Another object of the invention is to provide a device of this characterwhich is within a wide range, for example, from one inch of Water /g'fractions thereof, to pressures pounds per square inch.

Other objects will be apparent from the following specification.

This application is a division of my co-pending application, Ser. No.34,960, filed June 24, 1948.

In the drawing:

Fig. 1 is an end view of the device with parts broken away.

Fig. 2 is a View of the device with parts shown in section, taken online 2-2 of Fig. 1.

Referring to the drawings which illustrate the application of theinvention to a pressure gauge, the numerals designate mounting orbacking members provided with apertures 11 adapted to receive securingmeans for ana range of pressures pound per square inch) or in theneighborhood of 125 choring the same to a support or a casing. Themembers 10 support a body or housing having a large diameter cylindricalend portion 12 and a smaller portion 13 having a bore extending from endto end therethrough and preferably being of square or rectangular outercrosssectional shape, said parts interfitting and being fixedly securedtogether, as by welding, at 14. The end of the large diameter portion 12of the housing is spanned by an end plate 15 held in place by securingmembers or screws 16. The plate 15 preferably has a filling opening orport 17 formed therein normally sealed by a threaded plug or needlevalve 18. A gasket ring 19 is seated in a marginal recess at the mouthof the member 12 and is engaged and pressed upon by the plate 15 to forma seal at the joint between the casing parts 12 and 15.

The outer end portion of the cylindrical casing member 12 has anenlarged inner diameter providing an annular shoulder 20. A slackdiaphragm 21, which may be formed of rubber or other flexible material,seats at its margin against the shoulder 20, and a ring 22 bears againstthe outer face of said diaphragm and is secured to the casing member 12by the securing screws 23. The diaphragm member is spaced inwardly fromthe end such as variation in temperaadapted to measure pressures iii Eli

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plate 15 and cooperates therewith and with'the large diameter boreportion at the outer end of the member 12 to define a chamber 24. Thewall of the casing member 12 has a port 25 formed therein with which afluid pressure conduit 26 is connected, said conduit forming the sourceof supply of the fluid whose pressure is to be measured.

A thin walled metal tube 30, preferably formed of steel, fits within thebore of the part 13 and has a snug anchorage at 31 at its inner end. Thebore of the member 13 is slightly enlarged forwardly of the anchor point31 to provide a free clearance around the major portion of the tube at32. The tube 30 projects beyond the inner end of the casing part 13 andmounts an annular member 33 which is preferably formed of berylliumcopper or any other alloy selected, for purposes to be mentioned herein.The ring 33 is preferably shouldered at reduced portion 34 for firmanchorage with the outer end of the steel tube and preferably has afrusto-conical surface 35 formed concentrically therein at its outerface. A cup-shaped metal diaphragm 36 having a substantially cylindricalmarginal skirt portion 37 is mounted by the annulus or ring 33. In thepreferred form of the invention, the ring 33 has an annular orcylindrical groove 38 formed in its outer face concentric therewith toreceive and anchor the marginal portion of the diaphragm wall 37 so thatthe central part 36 of the diaphragm is spaced or ofiset from the ring33. The diaphragm 36, 37 is preferably formed from a metal having a lowcoefficient of expansion. The metal of which this diaphragm is formedand the metal of which the ring 33 is formed preferably have matchingcoefficients ofexpansion. A chamber 39 is formed within the casingmember 12 between the diaphragms 21 and 36. A bore 40 is formed in themember 12 to communicate with said chamber. Said bore preferably has atube 41 fitting therein with its outer end projecting outwardly from thecasing 12. The fit of the tube 41 within the passage 40 is preferably ashrink fit or any other fit which will insure against the leakage offluid around the outside of the tube. The chamber 39 is filled withliquid, such as oil, which is introduced therein through the tube 41.After the chamber 39 is completely filled with liquid, the outerprojecting end 42 thereof is sealed as by crimping and soldering or byany other suitable means. The outer end portion of the passage 40 isenlarged and screw-threaded at 43, and a protective cap 44 fits aroundthe projecting tube portion 42 and is threaded into the bore portion 43.

The rear or outer end of the small body portion 13 is spanned by a platesecured thereto by securing screws 51. The portion of the member 13 atthe rear or outer end thereof has a bore of larger inner diameter thanthe remainder of the bore of the member 13 to provide a shoulder 52against which bears the marginal portion of a slack diaphragm 53 whichmay be formed of rubber or any other material, preferably being the samematerial of which the diaphragm 21 is formed. The diaphragm 53 isclamped in place by a ring 54 secured to the casing portion'13 by thescrews 55. A passage 56 is formed in the member 13 outwardly of thediaphragm 53, said passage constituting an atmospheric opening. Theinner end of this passage is preferably reduced and screw threaded toreceive a screw-threaded member or plug 57 adapted to seal the deviceand to exclude dirt therefrom during shipment. device is in use.

A measuring element 60 is mounted in the space between the diaphragms 36and 53. This measuring element preferably constitutes an unbonded straingauge. A cup-shaped housing 61 has a marginal outwardly projectingtransverse flange 62 spans the mouth of the casing 61 and bears againstthe flange 62. Screws or other suitable securing members extend throughthe flange 62, the plate 63 and into the ring 33 to anchor the casingand associated parts to said ring. Any suitable type of strain gauge,preferably of the unbonded type may be mounted within the casing and hasa stem projecting therefrom. The forward end of the stem 75 has fixedlymounted thereon a fitting having an enlarged head 81. bearing flatagainst the inner face of the diaphragm portion 36 centrally of saiddiaphragm.

The plug 57 is removed when the at its mouth. A plate 63' An externallyscrew-threaded shank 82 projects outwardly through an. opening formedwithin the diaphragm. A nut 83 is threaded on said shank and serves tofixedly clamp the diaphragm to the. shank. In other words, the centralportion of the diaphragm around the opening through which the shank 82extends is firmly gripped and clamped between the nut 83 and the fittinghead 81. Jonsequently,any movement of the diaphragm 1S transmitted tothe stem and from the stem to the plate 72 of the strain gauge.

The casing portion 13 is provided with a plurality of passages extendingtherethrough and communicating with the space between the diaphragms 53and 36. Electrical leads 91 from the measuring element 60 will extendthrough suitable sheaths 92 mounted in the passages 90. A cup-shapedcasing 93 is fixedly mounted upon the casing part 13 rearwardly of thecasing part 12. This casing '13 preferably closed by a cover 94anchoredin place by the securing members 95 and pressing against a sealinggasket ring 96 which bears against the upper open cup-shaped housing 93.Within the cup-shaped housing 93 are mounted posts 97 which preferablysupport a partition 98. Posts 99 serve to space the partition 98 fromthe cover 94. Suitable terminals 100 mounted within the casing 93 andfixed resistors 101 are mounted upon the platform 98. Electrical leads.to the various components of the device may extend through a tubularneck 102.

In the operation of-thedevice, fluid, such as a'liquid or gas underpressure, which is subject to measurement, is transmitted from theconduit 26 through the passage 25 into the chamber 24 where it actsagainst the flexible diaphragm 21. The chamber 39 which is filled withliquid is subjected to the pressure in the chamber 24, and the oil orother liquid in the chamber 39 forms means for transmitting the pressureinthe chamber 24 to the measuring diaphragm 36. The diaphragm 36, beingformed from metal and preferably configured substantially as shown sothat it does not constitute a flat member, but instead has an offset endwall which is provided with encular concentric bends, is suflicientlyflexible to transmit the pressure to and through the stem 75 to actuatethe strain gauge 60. Observe that the chamber in which the straingaugeelement is located is filled witha non-conductive liquid, such as oil,and that this oil .is free to enter the space behind or within thediaphragm 36. Inasmuch as the range of movement of the diaphragm islimited, no problem of oil displacement is encountered. In actualpractice the full range of movement of the diaphragm is in the order of.001 inch. This movement is obviously so small as not to produce anysubstantial liquid displacement effect or problem, and any displacementwhich occurs is accommodated by the flexible diaphragm 53. In thepreferred form of the device,-the oil is retained within the .rear orinner portion of the part 13 to immerse the strain. gauge 60and isprevented from entering the chamber 93. In this connection the tubes 92,which pass through the openings 90 and lead the terminals or leads 91into the chamber 93, are'preferably projected into the housing 93 andcrimped-or otherwise sealed at 93', as best illustrated in Fig. 1.Theimmersion of the strain gauge in the oil insulates said gauge fromcondensate or other conductive moisture.

The shape of the diaphragm forms one of the important features of thisinvention. Observe that the cup-shaped form provides the cylindricalwall portion 37 to offset the transverse pressure measuring surface ofthe diaphragm from its mounting ring 33. The importance of thisconstruction is that it provides means for avoiding any error inmeasurement due to temperature effects, that is, from effects due to anydifference in the rate of response to changes of temperature upon thediaphragm 36, 37 and upon the ring 33. The mass of the ring 33 is muchgreater than the mass of the diaphragm, and this difference in mass,even in cases where the coefficient of expansion of the materials ofwhich the diaphragm and its mounting are formed are substantially equal,will tend to produce a difference in the rate of response of these partsto changes of temperature. Any difference occurring in this respect, dueto temperature eifects, can be absorbed by the cylindrical marginalportion 37 of the diaphragm. Thus a tendency of the ring 33 to expandradially or circumferentially compared to the diaphragm is absorbed andtaken up by the cylindrical diaphragm portion 37 which is free to flexradially without flexing the transverse end or Working portion 36 of thediaphragm.

It will be obvious that the construction herein illustrated,

wherein the sleeve 30 has clearance within its socket32 ring 33 totemperature effects without injury thereof or interference with theother working parts of the device. It may be mentioned that the effectof the difference of the rate of temperature response is minute andunder ordinary conditions in measuring devices would not be critical.However, where, as mentioned before, a strain gauge is used as themeasuring element and its full range of movement is in the neighborhoodof only .001 inch, the small or minute temperature effect becomescritical. Thus where the difference in temperature effects between thering and its mounting would be as low as .000001 inch, the same would bemeasurable by the instrument and would detract from its accuracy if thediaphragm unit were not constructed in a manner to compensatefor theeffect. that the mounting of a flat or substantially unskirted diaphragmwithin a mounting ring of greater mass would cause, when subjected tothe same temperature effects mentioned, a distortion or buckling of thediaphragm which would introduce an appreciable error in-the readingsobtained, due to the actuation of the strain gauge by this distorting orbuckling action.

The problem of compensation for errors arising as the result of changesin temperature is common. The arrangement of the parts, and particularlythe skirted character of the diaphragm 36, .the liquid immersion of thestrain gauge 60, and the location of the resistors 101 externally of theliquid chamber, serves to hold temperature errors to a minimum. Furthercompensation for any temperature errors which may occur can be providedby including, as a part of each of the fixed resistors 101, atemperature sensitive compensating resistor element. In this Way anelectrical temperature compensation, in addition and adjustment of suchtemperature sensitive mentioned above, is provided in the device. Itmight be mentioned in this connection that the use of such tem peraturesensitive compensating resistor elements is made possible by thelocation of those elements externally of the oil-filled chamber withinwhich the strain gauge or other transmitter is located. If the entireWheatstone bridge clrcuit were encased in the oil-filled chamber, theaddition and adjustment of such temperature sensitive resistors to thecircuit would present serious problems and would be impractical. The useof such temperature sens tive resistor elements outside of theoil-filled chamber is practical and feasible, however, and produces anincreased accuracy of response of thegauge to the fluid condition beingmeasured.

While the preferred embodiments of the invention have been illustratedand described herein, it will be understood that changes in theconstruction may be made within the scope of the appended claims withoutdeparting from the spirit of the invention.

I claim:

A diaphragm unit for use in a fluid pressure gauge comprising a rigidannulus, means mounting said annulus, and a cup-shaped metal diaphragmhaving an end portion and a skirt portion, said annulus fixedly mountingsaid diaphragm at the margin of said skirt portion and spaced inwardlyfrom the periphery of said annulus with said diaphragm end portionspaced from the adjacent surface of said annulus,'said annulus includinga central reduced portion projecting from the face thereof opposite theface confronting said diaphragm, and said mounting means constituting ametal tube encircling said reduced portion and projecting beyond theouter end thereof.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,630,292 Ely May 31, 1927 1,781,287 Mayo Nov. 11, 19301,870,904 Giesler Aug. 9, 1932 1,938,167 Baker Dec. 5, 1933 1,978,397Becker Oct. 30, 1934 2,036,582 Kollsman Apr. 7, 1936 2,447,261 Mock Aug.17, 1948 2,551,489 Eichmann May 1, 1951' It might be mentioned'in thisconnection\

